Piston



F. JARDINE Aug, 27, 1935.

PISTON Filed Nov. 15, 1928 vlNVENTO BY (3 QM E, M

ATTO NEYS Patented Aug. 27, 1935 UNITED STATES PATENT OFFICE PISTON Ohio, trustee Application November 15, 1928, Serial No. 319,484

6 Claims. (Cl. 309-) This invention relates to pistons and is particularly applicable to pistons made of aluminum, its alloys and other light materials, and adapted to be used in internal combustion motors and the like,

5 and is an improvement over the invention claimed in my co-pending application, Serial No. 312,429, filedOctober 15, 1928.

Aluminum and like materials have been used in pistons in internal combustion motors and possess many desirable characteristics, such as lightness in weight and high heat conductivity. However, when pistons of such materials are used in the ordinary cast iron cylinders of internal combustion motors these pistons, due to the high coeflicient of expansion of the material thereof, must be fitted with a large clearance when cold, in order that the pistons will not stick when hot, and this large clearance permits-slapping of the pistons when cold as while the motor is being heated up.

An object of the present invention is to provide a piston which may be made of material having a high coefiicient of expansion and which may be fitted with a large clearance in a cylinder having a low coefficient of expansion, so that the piston may expand freely and naturally without sticking when hot, and at the same time to prevent slapping of the piston while the engine is being heated up.

The word aluminum is used hereinafter to include this metal alone, its alloys, and other similar light metallic materials.

Other objects will hereinafter appear.

The invention will be better understood from the description of one practical embodiment thereof, illustrated in the accompanying drawing, in which:

Fig. 1 is a central longitudinal sectional view of a piston embodying the invention;

Fig. 2 is a central longitudinal section taken on the line II-II of Fig. 1;

Fig. 3 is a bottom plan view of a piston; and

Fig. 4 is a cross sectional view taken on the line IV-IV of Fig. 3, the lower half of the figure indicating the parts in their relative positions when hot, and the upper half indicating these parts in the positions they occupy when cold.

The piston shown comprises a head having a flat top i'surrounded by. a depending marginal flange 2 provided with piston ring grooves 3. A cylindrical skirt 4 is formed integrally with its head and connected thereto at both sides as illustrated at 5, the skirt being provided on its inner surface with wrist pin bosses 6, these bosses being connected to the head and flange 2 as by reenforcing webs I. The portions of the skirt intermediate the wrist pin bosses and constituting the bearing faces of the piston are separated from the head by slits or airgaps 8, while between the bearing faces the sides of the skirt are integrally joined to the depending flange of the head.

The skirt is first ground round and then the sides of the skirt for an extent of about sixty degrees to each side of the wrist pin axes are relieved by being ground eccentric to the axis of the piston. The purpose of the relief or eccentric grinding of the sides of the piston is as follows:

If the skirt were made circular and fitted with sufficient clearance in the cylinder it would, when the piston is cold, slap within the cylinder or cock out of line, damaging itself or the cylinder wall. If, however, the piston were-caused to move sidewise of the cylinder along the wrist pin axis, it would bear upon one element of the cylinder wall, which hearing would to some extent prevent slap by causing the piston to follow an arcuate path as the thrust was changed from one thrust face to another, the side of the piston skidding around on the curved wall of the cylinder. However, a bearing along only one element of the cylinder skirt would not sufficiently positively retain the 'piston with its axis parallel that of the cylinder and would permit the same to cock out of line almost as if it were free from all of the walls thereof. If, however, a bearing on two spaced elements of the walls of the skirt is provided, the piston is quite positively maintained with its axis parallel that of the cylinder, much in the manner in which a round piece of material may be held in V-blocks or angularly arranged jaws of a vise.

The piston may travel from the position having one bearing face engaging one side of the cylinder to that having the other bearing face engaging the diametrically opposite side by following an arcuate path bearing upon the side of the cylinder wall in the direction of the wrist pin axis, and will at all times be maintained against cocking out of line.

The means for causing the piston to move along the wrist pin axis and maintaining it, while cold, at one side of the cylinder consists of a bar or strut 9 of a material such as steel, invar, or the like, which has a co-efficient of expansion lower than that of the remainder of the piston. This bar or strut is positioned in the piston head in such a manner as to maintain one of the piston rings expanded so that it will contact the cylinder walls at both sides in the plane of the wrist pin axis. The bar passes through one side of the depending flange 2 of the piston head extending into one of the-piston ring grooves at It and has a reduced end! i which provides a shoulder l2 seating in the bottom of a counterbore It in the opposite side of the flange, the end of the pin being made hollow and riveted over as indicated at I4, just below the bottom of the lower ring groove 3. The other end of the pin is free to extend into the ring groove and maintain the lowermost piston ring in expanded condition. 0! course, the aluminum upon becoming heated expands at a greater rate than the bar, and when it has reached its operating temperature the piston ring may fit within the groove in the ordinary manner. However, upon contraction of the piston head, the ring, maintained in an expanded condition by the transverse bar, causes the piston to bear upon the side of the cylinder wall adjacent the riveted end of the bar making it move along its wrist pin axis toward this end and so travel in an arcuate path as the thrust is transferred from one thrust face to the other, and thus prevents slapping.

Of course, when the piston has become heated to operating temperature, it fits the cylinder with very little clearance so that slap is impossible, while its contact with the side of the cylinder wall prevents such slap while the engine is being heated up.

While I have described the illustrated embodiment of my invention in some particularity, obviously many variations and modifications thereof will readily occur to those skilled in the art to which this appertains, and I ,do not, therefore, limit myself to the precise details shown and de scribed, but claim as my invention all embodiments thereof coming within the scope of the subjoined claims.

I claim:

1. In an aluminum alloy piston, positive means maintaining one piston ring expanded with the side above one end of the wrist pin within its groove, to cause the piston to travel longitudinally of its wrist pin axis under the effects of temperature changes.

2. In an aluminum alloy piston, a diametrically extending strut parallel to the wrist pin axis of a material having a lower co-efiicient of expansion than the aluminum alloy, one end of the strut being secured to the metal of thepiston and the other extensible into one of the piston ring grooves.

3. In an aluminum alloy piston, having a head with a depending flange provided with piston ring grooves, an aperture extending diametrically of the head parallel to the wrist pin axis and having its ends in one of the ring grooves, a transverse bar of a material having a lower co-efiicient of expansion than the material of the piston within the aperture, one end of said bar being anchored to said piston against movement in one direction. a

4. In an aluminum alloy piston, a skirt having concentric bearing faces, wrist pin bosses intermediate the bearing faces, a portion of the skirt intermediate the bearing faces being eccentric to said faces and within the cylinder in which the surface of said faces lie, and positive means for maintaining one piston ring expanded to a pre determined clearance relation with a cylinder to translate the piston sidewise in the direction of its wrist pin axis.

5. In an aluminum alloy piston, a skirt having concentric bearing faces, wrist pin bosses intermediate the bearing faces, a portion of the skirt intermediate the bearing faces being eccentric to said faces and within the cylinder in which the surface of said faces lie, and rigid means maintaining one piston ring expanded to bear upon the wall of the cylinder in which the piston operates at one side thereof in the vertical plane of the wrist pin axis to positively move the piston against the opposite side of said cylinder wall when cool.

6. In an aluminum alloy piston, means for causing the piston to move along its wrist pin axis comprising an extensible member of a coefiicient of expansion lower than that of the material of the piston and adapted to bear upon the interior of a piston ring in the direction of said wrist pin axis, the member being anchored to the metal of the piston at a point opposite its bearing on said ring.

FRANK JARDINE. 

